|Message: Re: Identical track data from different simulations||Not Logged In (login)|
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Managing a pseudo-random number generator (PRNG) can be subtle. In particular, in Geant4 each event uses a different number of calls to the PRNG. So once some event in your second run just happens to start in the same place of the PRNG sequence as some event in the first run, from then on the sequences of events will be identical. Apparently for your case this is not as unlikely as it seems.
The default PRNG of CLHEP is very good, and guarantees no repeats within 900M calls for seeds between 0 and 900M. So what I do is seed the PRNG with the event number at the start of each event (it happens in GeneratePrimaries() before doing anything else except determine the event number).
I have never seen duplicate events, and I did look for them when I first wrote this code.
This has the side effect of being able to re-run a given event. So I can run a lot of events, generate histograms, and find some outlier events. I then re-run those specific events with visualization and can see just what happened.
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